Influence of envelope properties on interior insulation solutions for masonry walls

Energy efficiency in historical buildings with a worth-preserving appearance can be improved with interior thermal insulation. However, interior thermal insulation may change significantly the hygrothermal performance of the building envelope and increases the risk of moisture problems in the assembly components. This paper studies the influence of different wall structures, types of exterior render and brick and vapor control strategies on the moisture performance of internally insulated walls with vapor-open insulation for different climatic conditions in Switzerland. The hygrothermal performance is simulated with a coupled heat and mass transport model and evaluated using a hygrothermal indicator, called the RHT Index. The numerical analysis indicates that the hygrothermal performance of interior insulated walls depends mainly on the moisture performance of the exterior finishing render. A capillary active render with larger liquid permeability leads to higher moisture contents in the building envelope. The influence of parameters such as masonry structure and brick type on envelope hygrothermal performance is rather small. For wall envelopes with less capillary active renders, the need to use a vapor barrier depends on the risk for water leakage and the vapor resistance of the render.